A lens array (hereinafter abbreviated to "SLA") constituted by a number of parabolic refractive index distributing rod lenses which are arrayed to make their optical axes parallel has been used broadly to focus one-dimensional image information on the surface of an original document onto a contact type image sensor.
Recently, a so-called "perfect contact type image sensor" has been used, which is constituted by a contact type image sensor having light leading windows, so that an illuminating light source placed at the back side of this image sensor illuminates an original document though the light leading window, and an array of photo-detecting portions disposed close to the light leading windows detect reflected light from the original document. In such a case, the contact type image sensor and the original document are disposed so close together that an SLA is not required.
On the other hand, in an LED or liquid crystal printer, an SLA has been used to transmit, onto a photo-sensitive drum, light information expressed by the flashing of an LED array or the switching of a liquid crystal shutter array.
However, an SLA needs at least about 15 mm as a so-called focal length between a one-dimensional image information surface and a focusing surface. This value limits miniaturization of an apparatus using the SLA.
On the other hand, since the perfect contact type image sensor has no focusing system such as a lens or the like, there has been a problem that image information is faded on an image sensor if the distance between the image sensor and an original document becomes even slightly large. It is therefore necessary to maintain the sensor surface contact with the original document, so that there has been a problem that the sensor surface is apt to be damaged.